Apparatus for guiding medical tools have been shown to be of valuable assistance in various medical procedures, for example, manipulation of surgical tools, manipulation of cameras or sensors, biopsy, etc. An apparatus for guiding a medical tool usually also improves reproducibility compared to free-hand medical procedures, for example, surgical or biopsy procedures.
These apparatus typically have one or more degrees of freedom and may be manually driven in that the one or more degrees of freedom may be equipped with a brake with motive force being provided by a human practitioner, or may be automated in that at least one degree of freedom is driven by a computer controlled actuator.
A medical tool often needs to be oriented about a point in, on, or in proximity to a patient's body. However, having the main body of an apparatus that supports the tool located too proximal to the patient's body may be disadvantageous, since the supporting apparatus may, for example, interfere with the view of or access to the patient by the practitioner. An apparatus which can orient a tool about a remote fulcrum or remote center of motion can avoid such disadvantages.
The use of an apparatus that orients a tool about a remote center of motion is known in robotics as described, for example, in U.S. Pat. Nos. 5,397,323; 5,515,478; 5,630,431; 5,817,084; 5,907,664; 6,047,610; 6,246,200; and 7,021,173.
U.S. Pat. No. 5,397,323 to Taylor et al. discloses the remote center of motion principle in surgical robots with a first axis of rotation pointing into the remote center of motion, and a second axis materialized by a parallelogram mechanism implemented by two coupled parallel linkages of rigid bars and cylindrical joints. The two axes of the remote center of motion are orthogonal, and the mechanism operated around an upright initial (zero) direction.
Unfortunately, the parallelogram structure of Taylor et al. and other conventional parallelogram mechanisms is bulky, making it difficult to position with respect to a patient's body and in some cases forcing a patient to assume an uncomfortable or unconventional position. Therefore, there is a need for an alternative apparatus for guiding medical tools.
U.S. Pat. No. 5,817,084 discloses another exemplary linkage that provides a remote center of motion. The disclosed linkage arrangement allows the motors for positioning the insertion axis to be at a distance from the center of motion. However, the first motor is required to move the entire mass of the second motor in the disclosed linkage arrangement. This requires a larger first motor. The second motor sweeps out a volume as it is moved. Both of these shortcomings increase the mass and bulk of the disclosed linkage arrangement.
In certain applications it is desirable to provide a robotic manipulator device having an end effector that can pass through a small opening in a wall. One way this can be done is to introduce the end effector along an insertion axis with the axis constrained to rotate about a point substantially at the point where the insertion axis intersects the wall, which may be termed the center of motion for the insertion axis.
It will be appreciated that the position of the end effector can be expressed in a spherical coordinate system with an origin at the center of motion. The end effector position may be expressed as two angular displacements and a radius, which is the distance from the center of motion to the end effector. Thus the end effector can be positioned at any point within the range of motion of the robotic manipulator while passing through a small opening in a wall.
One application of such a robotic manipulator is the positioning of an end effector for performing surgical procedures. Minimally invasive surgery (MIS) provides surgical techniques for operating on a patient through small incisions using a camera and elongate surgical instruments introduced to an internal surgical site, often through trocar sleeves or cannulas. The surgical site often comprises a body cavity, such as the patient's abdomen. The body cavity may optionally be distended using a clear fluid such as an insufflation gas. In robotic minimally invasive surgery, the surgeon manipulates the tissues using end effectors of the elongate surgical instruments by remotely manipulating the instruments while viewing the surgical site on a video monitor. As previously mentioned, it may be impractical to place the motors for positioning the insertion axis in proximity to the center of motion. The robotic manipulator may include linkages to couple the motors for positioning the insertion axis at a distance from the center of motion.
The manipulator devices and methods disclosed herein provide advantages over those of the prior art.